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Half-life Knowledge-Based Practice

Chemistry · Nuclear Chemistry · Chemistry · Radioactive Decay & Nuclear Reactions

5 Chemistry practice questions on Half-life. Questions that assess core concepts and understanding.

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Questions

  1. 1.

    Two radioisotopes, X and Y, initially contain identical numbers of radioactive nuclei. If isotope X has a half-life of 6.0 hours and isotope Y has a half-life of 18.0 hours, what is the ratio of remaining nuclei of X to remaining nuclei of Y after 36.0 hours?

    • A) 1 : 4
    • B) 1 : 8
    • C) 1 : 16
    • D) 1 : 64
  2. 2.

    A sample of a radioisotope has a half-life of 15.0 hours. How much time must elapse for exactly 87.5% of the original sample to decay?

    • A) 15.0 hours
    • B) 30.0 hours
    • C) 45.0 hours
    • D) 60.0 hours
  3. 3.

    A radioactive sample of iodine-131 has a half-life of 8.0 days and currently contains 2.50 mg of the isotope. If the sample has been decaying for 32.0 days, what was the initial mass of iodine-131 present in the sample?

    • A) 20.0 mg
    • B) 40.0 mg
    • C) 10.0 mg
    • D) 80.0 mg
  4. 4.

    A sample of a radioactive nuclide decays so that only 6.25% of the original parent nuclei remain after 72.0 hours. What is the half-life of this radioisotope?

    • A) 4.50 hours
    • B) 9.00 hours
    • C) 12.0 hours
    • D) 18.0 hours
  5. 5.

    A sample of a radioactive isotope has an initial mass of 80.0 g and a half-life of 12.0 days. What mass of this isotope remains undecayed after 48.0 days?

    • A) 10.0 g
    • B) 5.0 g
    • C) 2.5 g
    • D) 20.0 g

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